九度oj 题目1019：简单计算器

题目描述：

    读入一个只包含 +, -, *, / 的非负整数计算表达式，计算该表达式的值。

输入：

    测试输入包含若干测试用例，每个测试用例占一行，每行不超过200个字符，整数和运算符之间用一个空格分隔。没有非法表达式。当一行中只有0时输入结束，相应的结果不要输出。

输出：

    对每个测试用例输出1行，即该表达式的值，精确到小数点后2位。

样例输入：

1 + 2
4 + 2 * 5 - 7 / 11
0

样例输出：

3.00
13.36

这道题采用两个栈，一个存储符号，一个存储数字
比较运算符的优先级以确定计算的顺序
一开始准备采用巧妙的办法来读取数字，代码如下

 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <string>
 #include <stack>
 #define MAX 202
 using namespace std;

 int cmp(char a, char b) {
     if(b == '+' || b == '-') {
         if(a == '+' || a == '-') {
             return ;
         }
         else if(a == '*' || a == '/') {
             return -;
         }
         if(a == '$') {
             return -;
         }
     }
     else if(b == '*' || b == '/') {
         return ;
     }
 }

 double cal(double a, double b, char c) {
     if(c == '+') {
         return a + b;
     }
     else if(c == '-') {
         return  a - b;
     }
     else if(c == '*') {
         return a * b;
     }
     else if(c == '/') {
         return a / b;
     }
 }
 stack<double> num;
 stack<char> sign;
 char temp[MAX];
 char calTemp[MAX];

 int main(int argc, char const *argv[])
 {
     gets(temp);
     int numTemp;
     int signTemp;
     sign.push('$');

     while(strcmp(temp,"") != ) {
         double ans = ;
         int ptr = ;
         int tlen = strlen(temp);
         char signTemp;
         int flag = ;
         while(ptr < tlen){
             sscanf(&temp[ptr],"%s",calTemp);
             if(temp[ptr] >= '' && temp[ptr] <= '') {
                 sscanf(&temp[ptr],"%d",&numTemp);
                 if(flag == ) {
                     num.push(numTemp);
                 }
                 else if(flag == ) {
                     num.push(numTemp);
                     double a = num.top();
                     num.pop();
                     double b = num.top();
                     num.pop();
                     char calSign = sign.top();
                     sign.pop();
                     ans = cal(b, a, calSign);
                     num.push(ans);
                     flag = ;
                 }
                 else if(flag == ) {
                     double a = num.top();
                     num.pop();
                     double b = num.top();
                     num.pop();
                     char calSign1 = sign.top();
                     sign.pop();
                     char calSign2 = sign.top();
                     sign.pop();
                     ans = cal(b, a, calSign2);
                     num.push(ans);
                     sign.push(calSign1);
                     num.push(numTemp);
                     flag = ;
                 }
             }
             else {
                 if(sign.size() ==  && cmp(sign.top(),calTemp[]) == -) {
                     sign.push(calTemp[]);
                 }
                 else if(cmp(sign.top(),calTemp[]) == ){
                     sign.push(calTemp[]);
                     flag = ;
                 }
                 else if(cmp(sign.top(),calTemp[]) == ){
                     sign.push(calTemp[]);
                     flag = ;
                 }

             }
             int clen = strlen(calTemp);
             ptr = ptr + clen + ;
         }
         while(num.size() >= ) {
             double a = num.top();
             num.pop();
             double b;
             if(num.size() != ) {
                 b = num.top();
                 num.pop();
             }
             else {
                 b = ;
             }
             char calSign = sign.top();
             sign.pop();
             ans = cal(b, a, calSign);
             num.push(ans);
             if(num.size() == ) {
                 break;
             }
         }
         while(num.size() != ) {
             num.pop();
         }
         printf("%.2lf\n", ans);

         gets(temp);
     }

     return ;
 }

但提交后run time error ，不明白是哪里出错了

后来修改为如下代码

 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <string>
 #include <stack>
 #define MAX 202

 int cmp(char aq, char bq) {
     if(bq == '+' || bq == '-') {
         if(aq == '$') {
             return ;
         }
         return -;
     }
     else if(bq == '*' || bq == '/') {
         if(aq == '*' || aq == '/') {
             return -;
         }
         if(aq == '$') {
             return ;
         }
         return ;
     }
 }

 double cal(double a, double b, char c) {
     if(c == '+') {
         return a + b;
     }
     else if(c == '-') {
         return  a - b;
     }
     else if(c == '*') {
         return a * b;
     }
     else if(c == '/') {
         return a / b;
     }
 }
 std::stack<double> num;
 std::stack<char> sign;
 char temp[MAX];
 char calTemp[MAX];

 int main(int argc, char const *argv[])
 {
     gets(temp);
     double numTemp;
     int signTemp;
     sign.push('$');
     while(strcmp(temp,"") != ) {
         int numTemp = ;
         int flag = ;
         bool isNum = false;

         int i = ;
         while(i < strlen(temp)) {
             while(temp[i] >= '' && temp[i] <= '') {
                 numTemp = numTemp *  + temp[i] - '';
                 i++;
                 isNum = true;
             }

             if(isNum == true) {
                 if(flag == ) {
                     num.push(numTemp);
                 }
                 else if(flag == ) {
                     double a = num.top();
                     num.pop();
                     char calSign = sign.top();
                     sign.pop();
                     double ans = cal(a, numTemp, calSign);
                     num.push(ans);
                     flag = ;
                 }
                 else if(flag == -) {
                     double a = num.top();
                     num.pop();
                     double b = num.top();
                     num.pop();
                     char calSign1 = sign.top();
                     sign.pop();
                     char calSign2 = sign.top();
                     sign.pop();
                     double ans = cal(b, a, calSign2);
                     num.push(ans);
                     sign.push(calSign1);
                     num.push(numTemp);
                     flag = ;
                 }
                 numTemp = ;
                 isNum = false;
             }
             else if(temp[i] != ' '){
                 flag = cmp(sign.top(),temp[i]);
                 sign.push(temp[i]);
                 isNum = false;
             }
             i++;
         }
         double a = num.top();
         num.pop();
         double b = num.top();
         num.pop();
         char calSign = sign.top();
         sign.pop();
         double res = cal(b, a, calSign);

         printf("%.2lf\n", res);
         gets(temp);
     }

     return ;
 }

一开始把 '==' 打成了 '='，结果出现了匪夷所思的错误，经过多次排查，终于发现错误。以后要注意！！！！！！！！！！！！

-----9-17更新

事实上，如果只有加减乘除的话，还可以采用下面的办法，用一个数组去存储加减的数，遇到乘除法先算出来再存到数组中，最后直接算这个数组中数的和，代码如下

 #include <cstdio>
 #include <cstring>

 char str[];
 double dealed[];

 int main(int argc, char const *argv[])
 {
     while(gets(str) !=  && strcmp(str,"") != ) {
         int len = strlen(str);
         int isP = ;
         int i = ;
         int p = ;
         int isM = ;//0 null ,1 * ,2 /
         double last = ;
         while(i < len) {
             double tmp = ;
             while(i < len && str[i] >= '' && str[i] <= '') {
                 tmp = *tmp + str[i] - '';
                 i++;
             }
             while(i < len && str[i] == ' ') {
                 i++;
             }
             if(isM == ) {
                 tmp = tmp * last;
                 isM = ;
             }
             else if(isM == ) {
                 tmp = last /tmp;
                 isM = ;
             }
             if(i < len) {
                 if(str[i] == '+') {
                     dealed[p++] = tmp * isP;
                     isP = ;
                 }
                 else if(str[i] == '-') {
                     dealed[p++] = tmp * isP;
                     isP = -;
                 }
                 else if(str[i] == '*') {
                     last = tmp;
                     isM = ;
                 }
                 else if(str[i] == '/') {
                     last = tmp;
                     isM = ;
                 }
                 i++;
                 while(i < len && str[i] == ' ') {
                     i++;
                 }
             }
             else {
                 dealed[p++] = tmp * isP;
             }

         }
         double ans = ;
         for(int i = ; i < p; i++) {
             ans = ans + dealed[i];
         }
         printf("%.2lf\n",ans);
     }
     return ;
 }